U.S. patent application number 11/419727 was filed with the patent office on 2006-09-07 for method for forming different liquid crystal twist angle.
This patent application is currently assigned to TOPPOLY OPTOELECTRONICS CORP.. Invention is credited to JING-YI CHANG, WEI-CHIH CHANG, DAI-LIANG TING.
Application Number | 20060197897 11/419727 |
Document ID | / |
Family ID | 36943775 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060197897 |
Kind Code |
A1 |
CHANG; WEI-CHIH ; et
al. |
September 7, 2006 |
METHOD FOR FORMING DIFFERENT LIQUID CRYSTAL TWIST ANGLE
Abstract
Different liquid crystal twist angles realize different
luminescence efficiencies for reflection and transmission regions,
respectively. Therefore, the difference of liquid crystal twist is
used in reflection and transmission region, respectively, of a
liquid crystal display to maximize their luminescence efficiency so
that the total luminescence may reach the optimum state.
Inventors: |
CHANG; WEI-CHIH; (MIAO-LI
COUNTY, TW) ; TING; DAI-LIANG; (MIAO-LI COUNTY,
TW) ; CHANG; JING-YI; (MIAO-LI COUNTY, TW) |
Correspondence
Address: |
LOWE HAUPTMAN BERNER, LLP
1700 DIAGONAL ROAD
SUITE 300
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOPPOLY OPTOELECTRONICS
CORP.
NO. 12, KE JUNG RD., SCIENCE-BASED INDUSTRIAL PARK CHU-NAN
350
MIAO-LI COUNTY
TW
|
Family ID: |
36943775 |
Appl. No.: |
11/419727 |
Filed: |
May 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10646122 |
Aug 22, 2003 |
6936686 |
|
|
11419727 |
May 22, 2006 |
|
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Current U.S.
Class: |
349/114 |
Current CPC
Class: |
G02F 1/133555 20130101;
G02F 1/133753 20130101; G02F 1/133757 20210101 |
Class at
Publication: |
349/114 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 10, 2002 |
TW |
91120659 |
Claims
1. A liquid crystal display comprising: a first substrate; a second
substrate; a liquid crystal layer interposed between said first
substrate and said second substrate; a pixel region having a
reflection region and a transmission region formed over said first
substrate; a continuous wave surface formed over said reflection
region and said transmission region; a reflection electrode formed
in said reflection region substantially located in a peak area of
said continuous wave surface; a transmission electrode formed in
said transmission region substantially located in a valley area of
said continuous wave surface; and an orientation layer formed over
said transmission electrode and said reflection electrode, wherein
said orientation layer formed over said transmission region has a
first orientation direction and said orientation layer formed over
said reflection region has a second orientation direction, and said
first orientation direction is different from said second
orientation direction.
2. The liquid crystal display of claim 1, wherein said first
orientation direction defines a liquid crystal twist angle between
about 10 degrees and 70 degrees in said transmission region.
3. The liquid crystal display of claim 1, wherein said second
orientation direction defines a liquid crystal twist angle between
about 70 degrees and 90 degrees in said reflection region.
4. The liquid crystal display of claim 1, wherein a first rubbing
force is applied to said orientation layer to define said first
orientation direction and a second rubbing force is applied to
selected regions of said orientation layer to change said first
orientation direction in said selected regions to said second
orientation direction.
5. The liquid crystal display of claim 4, wherein said first
rubbing force is larger than said second rubbing force.
6. The liquid crystal display of claim 1, wherein an UV light with
a first polarized direction irradiates said orientation layer to
form said first orientation direction.
7. The liquid crystal display of claim 6, wherein said UV light
irradiates said orientation layer from back side of said first
substrate and utilizes said reflection electrode as a mask.
8. The liquid crystal display of claim 1, wherein an UV light with
a second polarized direction irradiates said orientation layer to
form said second orientation direction.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 10/656,122, filed Sep. 8, 2003 which is based
on, and claims priority from, Taiwanese Application Number
91120659, filed Sep. 10, 2002, the disclosure of which is hereby
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of making liquid
crystal display (LCD), and more specifically, to a method of using
different liquid crystal twist angle in a LCD having both
reflection and transmission regions to reach the maximum light
efficiency.
BACKGROUND OF THE INVENTION
[0003] Recently, personal digital assistant (PDA) and notebooks
have progressed remarkably. Displays for portable use must be light
in weight and have low power consumption. Thin film transistor
liquid crystal display (TFT-LCD) can meet the above requirements
and are known as the display required for high pixel density and
quality. In general, a TFT-LCD includes a bottom plate formed with
thin film transistors and pixel electrodes and a top plate formed
with color filters. The space between the top plate and the bottom
plate is filled with liquid crystal. In each unit pixel, a
capacitor and a further capacitor are provided; these capacitors
are charged and discharged using the TFT as the switching element
of the unit pixel. When the data voltage is applied to the TFT, the
arrangement of the liquid crystal molecules is changed, thereby
changing the optical properties and displaying the image.
[0004] Because liquid crystal is not itself luminescent, there are
two types, transmission type and reflection type, of LCDs. A
transmission type LCD includes an illuminator called a backlight
disposed at the rear, which provides a light source. In such a
transmission type liquid crystal display device, however, the
backlight consumes a large portion of the total power consumed by
the liquid crystal display device. Further, in order to improve the
display quality in a bright environment, the intensity of the light
from the backlight needs to be increased. This further increases
the power consumption of the backlight and thus the resultant
liquid crystal display device.
[0005] In order to overcome the above problem, a reflection type
liquid crystal display device has been provided. Such a reflection
type liquid crystal display device uses a reflector formed on one
of a pair of substrates so that ambient light is reflected from the
surface of the reflector. Since the conventional liquid crystal
display of the reflection type use the ambient light for the
display, the display luminance largely depends on the surrounding
environment, and when used under the circumstances where the
ambient light is weak, the display content may not be observed. The
liquid crystal displays of the reflection type do not use back
light for the display, and therefore, have an advantage of saving
power.
[0006] In order to overcome the above problems, a construction
having both a transmission type display and a reflection type
display in one liquid crystal display device has been disclosed in
U.S. Pat. No. 6,195,140. Such a liquid crystal display device has a
different cell gap between the top plate and bottom plate in a
transmission region and reflection region to maximize the luminance
efficiency.
SUMMARY OF THE INVENTION
[0007] Because differences in liquid crystal twist angle may
realize different luminescence efficiencies, the main purpose of
the present invention is to provide a manufacture method of liquid
crystal display to employ different liquid crystal twist angles in
the reflection and transmission regions to maximize the total
luminance. The liquid crystal display of the present invention may
transmit a part of incident light and reflects the rest so that it
can be used when the ambient light is weak while maintaining the
advantages of the reflection type liquid crystal display.
[0008] The difference of liquid crystal twist angles may result in
the different luminescence efficiency for reflection and
transmission regions, respectively. Therefore, the difference of
liquid crystal twist angles will be respectively used in reflection
and transmission regions of a liquid crystal display to maximize
their luminescence efficiency. Concave and convex structures are
utilized in the lower substrate of the liquid crystal display in
accordance with the present invention.
[0009] In the first embodiment, a rubbing method is used to arrange
the orientation. A rubbing process adjusts and determines the
orientation of the orientation layer that may arrange the liquid
crystal molecules according to the determined orientation. The
present invention uses different rubbing pressures to adjust and
determine the orientation of the reflection region and transmission
region. A higher rubbing pressure is used to adjust and determine
the orientation of the transmission region. At this time, the
orientation of the reflection region is also rubbed in the same
direction. However, a lower rubbing pressure is used to adjust and
determine the orientation of the reflection region. Because the
transmission region is located in the recess of the concave and
convex structure, it is not rubbed in this step so that the
orientation of the transmission region is not changed in this step.
In other words, different rubbing pressure is used in this
embodiment to arrange the orientation. Both the transmission region
and the reflection region can be rubbed when using the higher
rubbing pressure. However, only the reflection region can be rubbed
when using the lower rubbing pressure. Therefore, there are
different orientation arrangements formed on the two regions.
[0010] The second embodiment uses UV light to adjust and determine
the orientation of the liquid crystal display. This method utilizes
UV lights with different polarized direction to illuminate the
orientation layer in the transmission region and the reflection
region respectively. Accordingly, a UV light with a polarized
direction that is same as the required orientation direction is
used to illuminate the orientation layer, wherein the UV light
source is located above the orientation layer. After illuminating,
the transmission region and the reflection region both have the
same orientation direction. Next, a UV light with a polarized
direction that is same as the required orientation direction of the
transmission region is used to illuminate the orientation layer,
wherein the UV light is located under the transmission region and
reflection region. Accordingly, an orientation layer is formed over
the transmission region and the reflection region. Therefore, when
the UV light is located above the orientation layer, the whole
orientation layer will be arranged. When the UV light is located
under the transmission region and reflection region, because the
reflection region is composed of an opaque material, the
orientation layer located above the reflection layer is not
illuminated by the UV light again. As a result, the transmission
region and the reflection region have different orientation
directions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0012] FIG. 1 is a schematic, perspective drawing of a conventional
liquid crystal display (LCD).
[0013] FIG. 2 is a schematic, cross-sectional drawing of a
conventional liquid crystal display (LCD).
[0014] FIG. 3 is a schematic, cross-sectional view of a liquid
crystal display in accordance with the present invention.
[0015] FIG. 4A is a schematic, cross-sectional view of a liquid
crystal display, wherein a reflection layer is formed over the
transparent conductor layer.
[0016] FIG. 4B is a schematic, cross-sectional view of an enlarged
region of a liquid crystal display in accordance with the present
invention.
[0017] FIG. 5 is an orientation arrangement diagram of the
orientation layer of the upper substrate in accordance with the
present invention.
[0018] FIG. 6A and FIG. 6B are orientation arrangement diagrams of
the reflection and transmission regions, respectively, in
accordance with the present invention.
[0019] FIG. 7A and FIG. 7B are schematic, cross-sectional views
showing use of differently polarized UV lights to form different
orientation arrangement diagrams in the reflection and transmission
region according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] Without limiting the spirit and scope of the present
invention, the method proposed in the present invention is
illustrated with one preferred embodiment about a manufacturing
method of liquid crystal display. Skilled artisans, upon reviewing
the embodiments, can apply the fabricating method according to the
present invention to any kind of liquid crystal display having
reflection and transmission region to maximize the
light-utilization efficiency in the two regions. The method of the
present invention transmits part of the incident light and reflects
the rest and can be used when the ambient light is weak while
maintaining the advantages of the liquid crystal displays of the
reflection type. The application of the present invention is not
limited by the following embodiment.
[0021] The difference in liquid crystal twist angle may cause
different luminescence efficiencies for reflection and transmission
regions respectively. In accordance with the present invention,
different liquid crystal twist angles will be used in reflection
and transmission regions respectively to maximize the luminescence
efficiency of the liquid crystal display so that the total
luminescence may reach the optimum state. In accordance with one
embodiment of the present invention, for a liquid crystal display
with a 4 .mu.m distance between the upper and lower substrates,
when the liquid crystal twist angle is between 70 degrees and 90
degrees, the reflection region has the optimum luminescence
efficiency herein, and, when the liquid crystal twist angle is
between 10 degrees and 70 degrees, the transmission region has the
optimum luminescence efficiency. Therefore, the whole luminescence
efficiency of a liquid crystal display will reach the optimum state
when the reflection region has a liquid crystal twist angle between
70 degrees and 90 degrees and the transmission region has a liquid
crystal twist angle between 10 degrees and 70 degrees.
[0022] The present invention will now be described in detail with
reference to drawings. FIG. 1 shows a schematic drawing of a thin
film transistor liquid crystal display (TFT-LCD). The liquid
crystal layer 104 is interposed between the upper glass substrate
100 and lower glass substrate 102. The lower glass substrate 102
includes signal line 106 and scan line 108 arranged in a matrix,
and in the area defined by the signal line 106 and scan line 108
there is a thin film transistor 110 and a transparent pixel
electrode 112. The common electrode 114 and color filter 116 is
arranged on the upper glass substrate 100. Then, the liquid crystal
display is placed between a pair of light polarizers 118 and 120.
When the light 122 is injected into the liquid crystal display, the
display will be a transmission type. Each pixel electrode 112 faces
a corresponding color filter with red, green or blue color.
[0023] FIG. 2 shows a schematic drawing of a thin film transistor
used in one embodiment of the present invention. A gate electrode
202 that is sequentially covered with two insulation layers 204 and
206 forms on a glass substrate 200. A channel region 208 fabricated
by amorphous silicon material is formed over the insulation layer
206, and a channel protection layer 214 deposited thereon to
protect the channel. The drain and source region 210 and 212
fabricated by doped amorphous silicon material located on the both
sides. An Indium-Tin-Oxide conductor layer 216 covers the drain and
source electrodes 210 and 212 and connects with the pixel electrode
(not shown in the figure).
[0024] FIG. 3 shows a side view of the liquid crystal display of
the present invention. The main difference between FIG. 1 and FIG.
3 is that the thin film transistor 110 in FIG. 3 is covered with an
insulation layer 126. A etch process is applied to the insulation
layer 126 to form concave and convex surfaces. A transparent
Indium-Tin-Oxide conductor layer 128 covers the insulation layer
126 and connects with the pixel electrode 112 of the thin film
transistor 110 through a hole 32. The common electrode 114 also
composed of the transparent Indium-Tin-Oxide material is formed on
the glass substrate 100.
[0025] FIG. 4B is an enlarged drawing of FIG. 3 that shows a
partial region of transparent conductor layer 128 of the present
invention. When both the reflection region and transmission region
want to be realized in a pixel, firstly, a reflection layer 152 is
formed over the transparent conductor layer 128 as illustrated in
the FIG. 4A. The material of reflection layer 152 is Al or Al/Mo
alloy. Next, a photoresist 150 is used to define a transmission
region in the reflection layer 152. Then, an etching process is
performed to form reflection electrode 144 as illustrated in the
FIG. 4B. The transparent conductor layer 128 of the transmission
region 132 is the transmission electrode. Finally, the photoresist
152 is removed. In accordance with this embodiment, the
transmission electrode is located substantially on the concave
surface. The defined reflection electrode is substantially located
on the convex surface. A plurality of reflection electrodes forms
the reflection region of the LCD. The result is shown in FIG. 4B,
wherein the block 130 is reflection region and the block 132 is the
transmission region. Next, orientation layer 134 is coated on the
surfaces of the reflection electrode 144 and the transmission
electrode. The orientation layer is also coated on the common
electrode 114. In general, the function of the orientation layers
is to control the orientation of the liquid crystal molecules. The
orientation layer 134 is formed by a polyimide.
[0026] In accordance with an embodiment of the present invention,
the whole luminescence efficiency of a liquid crystal display with
a 4 .mu.m distance between the upper and lower substrate will reach
the optimum state when the reflection region has a liquid crystal
twist angle between about 70 degrees and 90 degrees and the
transmission region has a liquid crystal twist angle between about
10 degrees and 70 degrees. The following is a description of the
methods in this invention to arrange the orientation of the liquid
crystal twist angle.
Rubbing
[0027] The rubbing method is used to arrange the orientation in the
first embodiment. The rubbing process adjusts and determines the
orientation of the orientation layer that may arrange the liquid
crystal molecules according to the determined orientation. The
present invention uses different rubbing pressures to adjust and
determine the orientation of the reflection region 130 and
transmission region 132, as shown in FIG. 4. For example, because
the transmission region 132 is located in the recess of the concave
and convex structure, the higher rubbing pressure is used to adjust
and determine the orientation of this region. The orientation is
adjusted and determined in the reflection region 130 and the
transmission region 132 at the same time due to the higher rubbing
pressure.
[0028] Conversely, because the reflection region 130 is located in
the convex portion of the concave and convex structure, the lower
rubbing pressure is used to adjust and determine the orientation of
this region. The transmission region 132 located in the recess of
the concave and convex structures is not rubbed in this step
because of the lower rubbing pressure so that the orientation of
this region is not changed in this step. Therefore, the two regions
have different orientations after the two rubbing steps, wherein
the transmission region 132 is only rubbed in the first rubbing
step but the reflection region 130 is rubbed in the two rubbing
steps. However, because of the rubbing characteristic that the
latter rubbing step determines the orientation, the second rubbing
step dictates the orientation of the reflection region 130. In
accordance with the preferred embodiment of the present invention,
the rubbing pressure applied to the transmission region 132 at
least may rub the lowest portion herein. Conversely, the rubbing
pressure applied to the reflection region 130 may not overlap the
transmission region 132.
[0029] In accordance with the preferred embodiment, a 60-degree
liquid crystal twist angle is required in the transmission region
132 and an 80-degree liquid crystal twist angle is required in the
reflection region 130. FIG. 5 shows a rubbing direction having a
45-degree angle with the vertical axis applied to the orientation
layer 134 over the common electrode 114. FIG. 6A and FIG. 6B
respectively show the rubbing direction applied to the orientation
layer 134 formed over the reflection region 130 and the
transmission region 132. FIG. 6 A is the rubbing of the
transmission region 132. Because the transmission region 132 is
located in the recession of the concave and convex structure, the
higher rubbing pressure is used to identify the orientation of this
region. The rubbing pressure applied to the transmission region 132
depends on the depth of the recession. In accordance with the
preferred embodiment, the 60-degree liquid crystal twist angle is
required in the transmission region 132. The rubbing direction
applied to the transmission region 132 is shown in the FIG. 6A
indicated by arrow 138. This direction has a 60-degree angle with
the rubbing direction (indicated by a dotted arrow) applied to the
orientation layer 134 formed over the common electrode 114.
[0030] FIG. 6 B shows the orientation arrangement of the reflection
region 130. Because the reflection region 130 is located in the
convex portion of the concave and convex structure, the lower
rubbing pressure is used to identify the orientation of this
region. The rubbing pressure applied to the reflection region 130
may not overlap the transmission region 132. Therefore, the
transmission region 132 located in the recession of the concave and
convex structure is not rubbed in this step. In accordance with the
preferred embodiment, the 80-degree liquid crystal twist angle is
required in the reflection region 130. The rubbing direction
applied to the reflection region 130 is shown in FIG. 6B and
indicated by arrow 140. This direction has an 80-degree angle with
the rubbing direction (indicated by a dotted arrow) applied to the
orientation layer 134 formed over the common electrode 114.
Therefore, the reflection region 130 and transmission region 132
have different orientation arrangements after the two rubbing
steps. The difference of the liquid crystal twist angle in the two
regions may realize the maximum luminescence efficiency.
[0031] The rubbing method, evaporation method and UV light
alignment method may also be used to arrange the orientation of the
orientation layer 134 formed on the common electrode 114.
UV Light
[0032] The second embodiment of the present invention uses the UV
alignment method. The method uses UV light having an identical
polarized direction to arrange the respective orientations of the
orientation layers formed over the reflection region 130 and
transmission region 132.
[0033] Referring to FIG. 7A, the orientation of the reflection
region 130 is first arranged. The UV light 142A having an identical
polarized direction as required orientation on the reflection
region 130 is used to arrange the orientation of the orientation
layer 134. Because the UV light illuminates the whole orientation
layer 134, the transmission region 132 and the reflection region
130 have the same arranged orientation.
[0034] Referring to FIG. 7B, the orientation of the transmission
region 132 is arranged next. The UV light 142B having an identical
polarized direction as the required orientation on the transmission
region 132 is used from the back to illuminate the orientation
layer 134 to arrange the orientation. Although the UV light also
illuminates the whole orientation layer 134, it does not illuminate
the orientation layer located over the reflection region 130 again
due to the reflection region 130 made by opaque material. Only the
orientation layer 134 over the reflection region 130 changes the
orientation in this step so that the two regions will have the
different orientation after the two illumination steps. The
reflection region 130 is only illuminated in the first arranged
orientation step but the transmission region 132 is illuminated in
the two arranged orientation steps. However, because of the
characteristic of using UV light to arrange the orientation of the
orientation layer, the latter polarized direction of the UV light
determines the orientation. After these two orientation arrangement
steps, an option step is performed. At this step, a thermal process
is performed to fix the orientation arrangement of the orientation
layer 134.
[0035] In accordance with the second embodiment, the rubbing
method, evaporation method and UV light alignment method may also
be used to arrange the orientation of the orientation layer 134
formed on the common electrode 114.
[0036] Although the invention has been described in detail herein,
with reference to its preferred embodiment, it is to be understood
that this description is by way of example only, and is not to be
interpreted in a limiting sense. It is to be further understood
that numerous changes in the details of the embodiments of the
invention can occur, and additional embodiments of the invention
will be apparent to, and may be made by, persons of ordinary skill
in the art having reference to this description. Such changes and
additional embodiments fall within the spirit and true scope of the
invention as claimed below.
* * * * *